New cat owner, general advice needed. :-)

I have a 6month old male kitten (due to be neutered at the end of the month) who sadly lost his brother (littermates) not long after I bought them home at 10 weeks. He was ok by himself but I felt guilty leaving him alone when at work so have found him a new companion, however his friend is a four year old female (spayed). She lived with another male cat who was her age and although it's only been 2 days she is adjusting ok, mostly hiding in the day and coming out at night but eating, drinking and using the litterbox and being affectionate when I see her.

There has been some hissing and growing which is to be expected but I did speak to the vet who before I got her and they recommended an older female as a companion for him. I just wanted to get some general tips and advice about settling her in and anything I might need to be aware of with them getting used to each other. She is currently isolated, etc but the vet said where my boy is still so young it would likely work out with her being top cat!

I just want them to both be happy and comfortable so please let me know if there's anything I can do to make the process better for them both.

Welcome to TCS. The best advice I can give you is to check out the articles section of this site. I like to think of it as an owner's manual for cats. Here is one that is most relevant to the integration of your new cat. www.thecatsite.com/a/introducing-cats-to-cats